Volume control system



Aug. 6, 1935.

G. P. ADAIR VOLUME CONTROL SYSTEM Filed July 3, 1931 6 Sheets-Sheet 'lIN V EN TOR.

40450 3, fldaiq BY 5 0 AT TORNEYY:

1935- G. P. ADAIR VOLUME CONTROL SYSTEM 6 Sheets-Sheet 2 i:

Filed July 3, 1951 Ivar- INVENTOR. ee/19w 3. Mai/v,

BY by ATTORNEY 1935. G. P. ADAIR VOLUME CONTROL SYSTEM Filed July 3,1951 6 Sheets-Sheet 3 Ilu- INVENTOR. em 5w 55' Wall/u,

6 ATTORNEY G. P. ADAIR Aug. 6, 1935.

VOLUME CONTROL SYSTEM Filed July 3, 1931 6 Sheets-Sheet 4 ATTORNEY 61935. G, ADAlR 2,010,002

VOLUME CONTROL SYSTEM Filed July 3, 1931 6 Sheets-Sheet '6 INVENTOR.Qwmgw .5, 91241430,

(2 ATTO RNEY Patented Aug. 6, 1935 PATENT OFFICE 2,010,002 VOLUMECONTROL SYSTEM George P. Adair,

San Antonio, Tex.

Application July 3, 1931, Serial No. 548,695

6 Claims.

(Granted under the act of March 3, 1883, as

amended April 30,

My invention relates broadly to volume control systems and moreparticularly to a circuit arrangement for automatically controlling thecoupling of the electrical circuits in a radio receiving system forcorrespondingly controlling the volume of the reproduced sound.

One of the objects of my invention is to provide a circuit arrangementfor reducing fading effects in radio broadcast receiving circuits byautomatically controlling the coupling of the circuits in the receiverin accordance with the amplitude of the incoming signaling energy.

Another object of my invention is to provide a volume control circuitfor radio broadcast receivers which operates independent of frequencyfor maintaining the volume of sound reproduced by the radio broadcastreceiver constant independent of fading effects.

Still another object of my invention is to provide a device forcontrolling the coupling of the circuits in a radio broadcast receiverat the same time indicating conditions of resonance of the receivingcircuit for the reproduction of sound at constant volume independent offading efi'ects.

A further object of my invention is to provide a construction ofmechanical actuator for controlling the volume of reproduced sound inaccordance with variable conditions of fading in the circuits of theradio broadcast receiver wherein the parts are arranged to avoidappreciable wear and to give gradual control over the entire range ofthe receiving apparatus.

Other and further objects of my invention reside in the circuitarrangement for and the construction of the variable coupling deviceused in association with the amplifier circuits of a radio broadcastreceiver as set forth more fully in the specification hereinafterfollowing by reference to the accompanying drawings, in which:

Figure 1 illustrates one circuit arrangement for a radio broadcastreceiver equipped with a volume control circuit in accordance with myinvention; Fig. 2 shows a modified form of variable coupling systememployed in interstage relationship in an amplifier system embodying myinvention; Fig. 3 shows a simplified form of radio receiving circuitincluding a variable coupling device for controlling the transfer ofenergy through the amplifier in accordance with my invention; Fig. 4illustrates an electrostatic control apparatus for varying the couplingbetween the stages of an amplifier system in accordance with myinvention; Fig. 5 shows an arrangement of automatic coupling controlapparatus in which the inductive association of the coupling coils in anamplifier system is variably controlled in accordance with the amplitudeof the incoming signaling energy; Fig. 6 is a schematic view showing amodified form of coupling control mechanism which may be employed in thecontrol system of my invention; Fig. 7 illustrates a further modifiedform of coupling control mechanism embodying the principles of myinvention; Fig. 8 illustrates another form of variable capacity deviceoperative in accordance 10 with changes in amplitude of signaling energyfor correspondingly controlling the amplification characteristics of thereceiving apparatus for governing the volume of the reproduced sound;Fig. 9 shows a further form of coupling control mechanism which may beemployed in the circuits heretofore described; Fig. 10 illustrates astill further modified form of variable capacity mechanism controllablein accordance with the operation of the signal receiving circuits in thesystem of my invention; and Fig. 11 shows a further modifiedconstruction of variable capacity control device employed in the fadingcompensator of my invention.

The volume control system of my invention is adaptable for installationin existing types of radio broadcast receivers. The coupling controlmechanism may be assembled as a separate unit and incorporated inexisting equipment at very reasonable cost. The control circuit of myinvention may be built into the radio receiving apparatus as part of theproduction program thereof at very reasonable cost. The controlmechanism of my invention comprises a variable impedance device, theeffective value of which is electromagnetically or electrostaticallycontrolled in accordance with the amplitude of the incoming signalingenergy. The operation of the variable impedance device is so damped thatthere is no tendency toward amplitude distortion. The effectivevariation in impedance may be made as fast as desired to meet specialconditions. I may arrange the variable impedance device intermediate thestages of amplification or the variable impedance devices may bearranged between antenna and the amplification circuit of the receiver,or etween the amplifier system the sound reproducing circuit.

In applying the volume control system of my invention to existing typesof receiving circuits, all voltages and currents of the high frequencycascade circuit remain unchanged so that they may be adjusted formaximum efficiency thereby reducing to a minimum signal distortion andso called cross-modulation due to improper adas illustrated.

justment of tube voltages which is inherent in voltage changing controlcircuits. the variable impedance system of my invention to existingreceiving circuits there is no tendency for the receiving circuit oramplifier to oscillate or flutter as is the case with other systems ofvolume control. The system of my invention provides automatic controlover a much wider range of signal strength than has been possible withprevious volume control systems. The volume control device of myinvention operates independent of frequency oi the actuating signal.

Referring to the drawings in more detail, reference character 6designates the input terminals of the receivin apparatus which includesa high frequency amplifier stage 2, the output .of which is connected tothe high frequency rectifier stage 3 through a variable coupling system.The output circuit of the high frequency amplifier tube 2 connects tothe input circuit of a control tube t as will be hereinafter describedin detail. The coupling system enclosed within the dotted line i d isactuated under control of the control tube 5 for'variably controllingthe transfer of energy to the high frequency rectifier tube 3.

The input circuit l connects through coupling condenser l3 andselectively tuned circuit 5 to the control grid '20 and the cathodeelement 27) through the ground connections 52. The output circuit oftube 2 connections from anode 2d to the input circuit of control tube tthrough condenser iii to control grid to. The anode potential for tube 2is supplied through choke coil '5 and regulating resistance it whichleads to the positive terminal or" the anode potential. A by-passcondenser 9 connects across the anode potential source to ground it asshown. A suitable biasing potential is supplied to the grid of controltube 3 0 through resistance i l. The heater cathodes 2a oftube 2, do oftube l, and 3a of tube 3, are suppliedwith heating current throughcircuit 5' from any suitable potential source. The output circuit ofcontrol tube t connects from anode id to the winding ll on the rotatablearmature it of the electromagnetic device forming part of the controlapparatus within the dotted line it. The armature iii is pivotallymounted for rotation between the magnetic polepieces of the magneticsystem 55. Rotatable armature it carries the movable pointer orindicator is which is normally biased by means of the spring 59 tooccupy the full line position shown in Fig. l. The pointer or indicatoris has one end thereof movable over a graduated scale 26}. The other endof the indicator or pointer 58 carries the plate member 23 by means ofarm 22 in insulated relation to the indicator r pointer it? throughinsulated joint ii. The plate 23 is electrically connected throughflexible conductor (-5 with the control grid 3c of the high frequencyrectifier tube 3. The plate member 23 may be capacitatively related toeither fixed plate or fixed plate 25. The capacity area 25 is connectedto ground '2 as shown while capacity area 2% connects to the outputcircuit of high frequency amplifier tube 2 at the anode 2d The inputcircuit of high frequency rectifier tube 3 is selectively tuned bycircuit 3% one end of which is connected to control grid 50 and to themovable capacity area 23 through flexible lead and the other end ofwhich is connected to ground, completing the circult to the cathode 3bof the high frequency rectifier tube 3'. In order to furnish therequired operating potential on the several electrodes of the tubes, Iprovide the resistance'elements 25, El,

In applying energy from tube 2 ferred to the grid 3c of the detectortube 3.

33, 37, 38 and 58 as shown. I also arrange suitable capacities 29, lii,4!, as, at, $3 and ll as shown. The anode potential for the tubes 3 andt is supplied from terminals 35 across by-pass condenser 35. The outputfrom the high frequency rectifier tube 3 leads from anode 3d throughcondenser 2 to output terminals -38 as shown.

In the operation of my volume control system as illustrated in Fig. l,variations in the amplitude of the incoming signaling energy due tofading conditions are caused to slowly modify the amplitude level of thespace discharge in the tube 2. This in turn, reacting upon the condenseriii produces variations in the potential applied to the grid of the tubeii, thereby controlling the flow of current in the armature winding llwhich is in the output circuit of tube At the extreme of fadingconditions the output signaling is for the most part trans- LIDdiminished and the strength of the signal applied to the grid 30 iscontrolled.

In Fig. '2 I have shown the application of the circuit arrangement of myinvention to a screen grid amplifier and high frequency rectifiercircuit.

In this arrangement high frequency amplifier tube 2' includes a screengrid 26 which is biased from the potential source 35 through regulatingresistance 28 having-a by-pass circuit to ground through condenser 36.High frequency rectifier tube 3 includes the screen grid element towhich .is biased from potential source 35 through resistance 3! having apath to ground through condenser 32 connected therewith as shown. Thehigh frequency amplifier tube 2 has its grid 20 biased to such valuethrough. resistances-iii, 3'1, 38 and 39 that the tube 2' operates onthe lower knee of the characteristic plate current curve. When a signalof a value greater than that required to give the desired output isimpressed on the system the plate current in the output of tube 3 isincreased thereby increasing the energi- Zation of actuating winding iiand decreasing the capacitative coupling between high frequencyamplifier tube 2 and high frequency rectifiertube by shifting capacityarea 23 out of juxtaposition with capacity area thereby maintaining theoutput the same as it was originally or as nearly so as desired. Thedegree of control depends upon the adjustment of the condenser ii! andthe bias on grid 30 of control tube 5 through bias resistance ii. Thecontrol also depends on the shape, dimensions and characteristics of thecoupling device. In order to secure extreme accuracy in operation ofcontrol tube 5. a manual adjustment may be provided at the input circuitof control tube 4 for obtaining the most satisfactory results from thesystem as a whole. The use of the grounded capacity area 25 is for thepurpose of making the rate of change of coupling greater and alsopreventing signal pick-up from any source other than through tube2.

' I While I have shown the grounded capacity area I realize that othermodifications may be employed and I do not intend that my invention be'limitedto the precise arrangement shown.

In Fig. 2 the dotted line position |8b of the indicator l8 shows oneextreme condition where maximum coupling between the output of highfrequency amplifier tube 2 and the input of high frequency rectifier 3'exists. The dotted line position l8a of the indicator represents acondition where minimum coupling exists between the output of highfrequency amplifier tube 2' and the input of high frequency rectifiertube 3.

Fig. 3 shows a simplified arrangement of volume control circuit wherethe control tube 4 connects directly in the input circuit to thereceiver. The input circuit of the first radio frequency amplifier stage2 is capacitatively coupled through the relatively movable plates 23 and24 with the tuned input circuit 50 of the receiver. I have illustratedthe receiver connected to antenna 5| and ground 52, the antenna circuitincluding primary winding 53, electromagnetically coupled with asecondary winding forming part of the tuning circuit 50. A tap is takenfrom the tuned input circuit 513 to the variable condenser ID in circuitwith the grid 40. The winding ll of the electromagnetic device isconnected as heretofore described in the output circuit of control tube4. The fixed plate 24 of the variable capacity system connects to oneside of the tuned circuit 53. The fixed plate 25 connects to ground l2as shown. The flexible lead 45 connects the movable capacity area 23 tothe control grid 20 of the high frequency amplifier tube 2 as shown. Thedesired potentials for the tube electrodes are obtained by means ofresistors 26, 21, 55 and 51. Condenser 51 is connected in shunt withresistor 56 as shown. The tuned circuit 5 is connected to the input ofthe high frequency amplifier tube 2 as shown. The maximum couplingcondition is shown in full line position. When the signal strengthincreases the plate current for control tube 4 increases therebyshifting arm l8 and decreasing the capacity coupling between electricalcircuit 50 and tuned circuit 5. Plate potential for tube 2 is obtainedthrough impedance elements 1 and 8 which lead to the source of platepotential. The output terminals 60 lead to the succeeding stage of highfrequency amplification or to a high frequency rectifier.

In Fig. 4 I have shown a modified form of circuit embodying my inventionin which the electrostatic attraction and repulsion between plates 23-44is utilized for changing the effective coupling between the output ofhigh frequency amplifier tube 2 and the input of high frequencyrectifier tube 3. In this arrangement the arm I8 is pivotally mountedand biased by means of spring I!) and carries movable plate 23 which maybe shifted from juxtaposition with respect to fixed plate 24 to aposition adjacent fixed plate 25. The circuit from the output of controltube 4 leads through radio frequency choke coil 6| to the indicator orpointer l8 to which movable plate 23 is directly connected. The platepotential. for control tube 4 is supplied tnrough resistance 26 andradio frequency choke coil 62 from the source of potential 35. Condenser12 is disposed in series between one side of the choke coil 62 whichconnects with arm I 8 and movable capacity area 23 and the tuned circuit36. The required operating potential for cathode 3b is supplied throughresistance 63. Under conditions of fading the signal strength varies inthe output circuit of high frequency amplifier 2. The bias is arrangedon 4c so that the control tube 4 is operating on the upper knee of thecharacteristic curve and an increasing signal reduces the plate circuit.As the signal strength increases above a predetermined value, the platecurrent or tube 4 decreases and the charge on movable condenser plate 23increases in like polarity to the charge on fixed plate 24, resulting inthe repulsion of plate 23 which moves to the dotted line position 23athereby decreasing the capacity between plates 23 and 24 and decreasingthe coupling between high frequency rectifier tube 3 and high frequencyamplifier 4. When the current strength rises in the plate circuit oftube 4 the charge of plate 23 is smaller, thereby decreasing therepulsion force and enabling the plate 23 to automatically resume thefull line position shown, restoring the normal coupling relationship.

In Fig. 5 I have shown a modified form of the circuit of my invention inwhich an electromagnetic coupling system is employed. In thisarrangement I have shown the input circuit of high frequency amplifiertube 2 completed through suitable potential source 64 for supplyingpredetermined bias potential on the grid 20 of tube 2. The control tube4 has the grid electrode 40 thereof biased from suitable potentialsource 65. The output circuit of control tube 4 connects in the mannerheretofore described through winding ll of the magnetic actuator. Theindicator arm it of the magnetic actuator and the shafts 66 and 6! aremechanically coupled one to another by electrically insulating couplings2| or 68 as shown. The shaft 66 carries variometer windings which areinductively related to the inductance 75 which connects to the input ofthe high frequency rectifier tube 3. The shaft 51 carries varicmeterwindings l inductively related to the inductance IS. A control circuitincluding shunt connected impedance Ha connects across the inductance 10for effecting adjustment of and compensating for changes in inductancein the coupling system. The output circuit of high frequency amplifier 2is completed through the inductances comprising variometer 69. Byvarying the spacial relation of the sets of inductances 59 and it withrespect to inductance I the coupling between the output of highfrequency amplifier 2 and the input of high frequency rectifier 3 isvaried. Condenser i5 is employed to tune inductance l5. As the currentin the plate circuit of control tube 4 increases the coupling betweeninductances 59 and 7B and inductance T5 is decreased, therebymaintaining the output current at terminals 48 substantially constant.

The variable capacitative device which I have heretofore described forcontrolling the coupling between different portions of the circuit maytake many different forms. I have illustrated a number of such forms inFigs. 6 to 11. In Fig. 6 the rotatable armature l6 carries a shaftmember to which there is attached a spider Tl carrying separate capacityareas 18, 19 and 30 displaced approximately 120 and adapted to shiftangularly within set of stationary capacity areas displaced 60" apart.Each stationary capacity area is displaced 60 from the adjacentstationary capacity area. The adjacent capacity areas belong todifferent sets. One set of stationary capacity areas is indicated byreference character 8| connected to bus connector 84. The output circuitof one of the coupling systems connects between terminal 85 and groundl2. The succeeding circuit 36 to which energy is to be transferred isconnected between ground l2 and the capacity areas 18, 19 and 8!]. Tnemotive mechanism for driving the sets of movable plates is actuated inthe manner heretofore described.

In Fig. 'l I have shown a multiple set of rotor plates 83 mounted uponshaft 22 extending from insulated coupling 2i which plates are adaptedto. be variably interleaved with oppositely disposed sets of multiplyarranged stator plates. One set of stator plates is represented at 8'?connected with the circuit from which energy is to be transferredthrough lead 85. The other set of stator plates is represented atBSconnected to ground l2. By moving shaft 22 so that plates 83 overlapto a maximum extent with plates 8?, the transfer of energy to tunedcircuit 3Eiis increased to a maximum. However by moving rotor plates 86to a position where the overlap is a minimum the transfer of energy is aminimum. The plates 86 are automatically actuated in the mannerheretofore described. I

In Fig. 8, I have shown a form of variable capacity device wherein themovable capacity area is in the form of 'a rod member 89 curved aboutthe center of angular movement as shown. The stationary capacity areasare shown at 9,8 and ill in the form of tubes concentrically disposedabout the movable capacity area 89. The actuation of the movablecapacity area is brought about in the manner described in connectionwith the previous figures.

In order to increase the stability of the variable capacity couplingdevice I may employ an arrangement as shown in Fig. 9, wherein a movableindicator arm i8 is linked through insulated coupling 2i with theconnecting rod 92 which connects with piston 93 in cylinder 94. Cylinder94 connects through tube 95 with the riser 936 which is concentricallysurrounded by the tubular ca-' pacity area 9? in spaced relation toriser 96. Movement of indicator 'armit by reason of the actuation of theelectromagnetic mechanism tends to displace the mercury in cylinder atto variably fill the riser 96 thereby controlling the eifective capacitybetween the coupling connection 85 leading from theinput system and thecoupling connection 65 leading to the output system.

In lieu of the rotary electromagnetic actuating mechanism I may employ asolenoid actuator having an actuating coil 98 as shown in Fig. 10, theactuating coil being connected in the output circuit of the control tubein a manner similar to the connection of the winding H. is operated bysolenoid winding 98 to move longitudinally extending shaft we to theright or left, thereby displacing the tubular capacity area iti withrespect to the fixed concentric cylinders 32 and H33. The amount ofdisplacement is measured by indicator if! operative over scale I85. Theinput system is connected through lead 85 withcap'acity area 562. Theoutput system is connected through lead 55 with tuned circuit 35.

Maximum transfer of energy occurs between leadstb and when capacity areaIt is shifted concentrically within capacity area Hi2. Minimum transferof energy occurs when capacity area lBl is shifted concentrically withincylin- Armature 98' systems may be used for controlling the couplingbetween different circuits in accordance with conditions existing in thecircuits. Ihave found the system of my invention as described hereinhighly practical and while I have described my invention in certainpreferred embodiments, I desire that it be understood that modificationsmay be made and that no limitations upon my invention are intended otherthan are imposed by the scope of the appended claims.

The invention herein described may be manufactured and used by and forthe Government of the United States of America, for governmentalpurposes, without the payment of any royalties thereon;

What I claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

1. In a signal receiving system, the combination of a signal receivingcircuit, an electron tube system, a'control tube connected with saidsignal receiving circuit, variable coupling means interposed betweensaid signal receiving circuit and said electron tube system, andelectrostatic means controlled from the output of said control tube foractuating said variable coupling means in accordance with conditionsexisting in the output of said control tube for variably controlling thetransfer of energy from said signal receiving circuit to said electrontube system.

2. In a signal receiving system, a signal re ceiving circuit, anelectron tube system, a control tube operated from said signal receivingcircuit, and electrostatic means controlled by the output of saidcontrol tube for varying the coupling between said signal receivingcircuit and said electron tube system in accordance with conditions insaid signal receiving circuit.

3. In an amplifier system, apliirality of elec-' tron tubes each havinginput and output circuits, a control tube connected to'the outputcircuit of one'of said electron tubes, a movable actuator operated by'said control tube, a resonance indicator controlled by said movableactuator, a movable condenser plate shiftable to different positions bysaid movable actuator and connected with the input circuit of asucceeding electron tube, a stationary condenser plate connected withthe output circuit of theprcceding electron tube, an independentstationary condenser plate positioned opposite said first mentionedstationary plate and connected to ground potential, said movableactuator operating to shift said movable condenser plate throughpositions adjacent or intermediate said stationary condenser plates forcontrolling the transfer of energy from the preceding electron tube tothe succeeding electron tube in accordance with the characteristics ofthe signaling energy in the circuits of the preceding electron tube. V

4. An amplifier system comprising a plurality of electron tubes eachhavinginput and output circuits, control means connected with the outputcircuit at one of said electron tubes, a movable actuator operated bysaid control means, said movable actuator carrying a resonance indicator and a movable capacity area shiftable to either of two limitingpositions, the stationary capacity areas disposed adjacent each of thelimiting positions of said movable capacity area, one of said stationarycapacity areas being connected tothe output circuit of one of said elec-V tron tubes and'said movable capacity area being connected to the inputcircuit of the succeeding electron tube, the other of said stationarycapacity areas being connected to ground, said movable actuatoroperating to variably shift said movable capacity area intojuxta-position with either or" said stationary capacity areas inaccordance with the operation of said control means for variablycontrolling the coupling between said electron tubes.

5. In an amplification system, a plurality of electron tubes each havinginput and output circuits, a control circuit connected with the outputcircuit of one electron tube, a pivotally mounted arm carrying acapacity area connected in the output of said control circuit andshiftable to either of two limiting positions, a stationary capacityarea disposed adjacent the path of said movable capacity area at theopposite limits of movement of said movable capacity area, one of saidstationary capacity areas being connected with the output circuit of oneof said electron tubes, the other of said stationary capacity areasbeing connected to ground and said movable capacity area being connectedto the input circuit of the succeeding electron tube, means for applyingcharges of the same polarity to said first mentioned stationary capacityarea and said movable capacity area, the magnitude of said charges beingvaried in accordance with the operation of said control means incorrespondence with the characteristics of signaling currents in thecircuits of said preceding electron tube for repulsively controlling thespacial relation between said movable capacity area and said firstmentioned stationary capacity area and correspondingly con trolling thecoupling between said electron tubes.

6. In a volume control system for radio receiving circuits having aplurality of successively coupled stages, means for impressing upon oneof said stages incoming signaling energy the amplitude level of whichvaries according to existing fading conditions, means controlled byamplified output energy derived from the particular stage last describedfor varying the coupling between said stage and a succeeding stage, saidlast mentioned means comprising a stationary capacitive elementconnected with the output circuit of one of the stages, a movablecapacitive element connected with the input circuit of the succeedingstage and a stationary grounded capacitive element adjacent the firstsaid stationary capacitive element for maintaining a substantiallyuniform reactance between said movable capacitive element and thestationary capacitive elements in different positions of said movablecapacitive element.

GEORGE P. ADAIR.

